In conventional permanent magnet synchronous rotary machines, magnets that function as a magnetic field means are mounted to a rotor. However, in motors that are used in “electrically assisted turbochargers” in which the motor is disposed between a turbine and a compressor of an automotive supercharger, super-high-speed rotation that exceeds 100,000 revolutions per minute is required, and since they are used in high-temperature environments, problems with magnet holding strength, thermal demagnetization, etc., arise if conventional permanent magnet synchronous rotary machines are used in these motors.
In consideration of these conditions, conventional magnetic inductor rotary machines have been proposed in which a magnetic field source such as a permanent magnet or a coil, etc., is disposed on a stator, and a rotor is configured such that cores to which gearwheel-shaped magnetic saliency is applied are disposed so as to be adjacent in two stages axially so as to be offset circumferentially by a pitch of half a pole (see Patent Literature 1 and 2, for example). These rotors are constituted only by a core that has a simple shape, and are superior in resistant strength against centrifugal forces when rotated at high speed. Thus, conventional magnetic inductor rotary machines make use of the advantages of these rotors, and it is conceivable that they could be used in high-speed motors such as electrically assisted turbochargers, etc.
Stator coil winding methods in conventional magnetic inductor rotary machines include distributed winding methods in which one coil per phase is wound so as to span a plurality of slots, and each of the phases of coil and coil ends have overlaps that cross in a circumferential direction (Patent Literature 1, for example), and concentrated winding methods in which one coil per phase is wound onto teeth so as not to span the slots, and none of the phases of coil and coil ends have overlaps that cross in a circumferential direction (Patent Literature 2, for example), and the rotor field methods include coils (Patent Literature 2, for example), and permanent magnets (Patent Literature 1, for example). In principle, combining the two stator coil winding methods and the two rotor field methods is unrestricted.
In conventional magnetic inductor rotary machines, because a rotating shaft of the rotor is rotatably supported by bearings that are disposed at two axial ends of the rotor, “axial resonance”, in which the rotating shaft constitutes a resonance system and flexes and vibrates, is problematic. The longer the interval between the bearings, and the faster the rotational speed of the rotor, the more likely that this axial resonance is to arise, and in the worst cases, the rotor will contact the stator.
Now, restricting the interval between the bearings to increase the rotational speed at which axial resonance arises is effective as a countermeasure to avoid contact between the rotor and the stator during super-high-speed rotation. Due to constraints of resistant strength against centrifugal forces, rotor diameter is reduced, stator diameter is reduced together therewith, and distance of the coil ends of the stator coil from the central axis of the rotating shaft is shorter. On the other hand, increasing the diameter of the bearings is desirable from the viewpoint of securing rigidity and of securing an oil cooling flow channel. Consequently, if the bearings are disposed radially inside the coil ends of the stator coil, problems of interference between the bearings and the coil ends of the stator coil arise. Thus, shortening axial length of the coil ends of the stator coil as much as possible is effective in order to avoid interference between the bearings and the coil ends of the stator coil, and reduce the distance between the bearings.
From the above, in order to apply magnetic inductor rotary machines to applications in which high-speed rotation is required, it is desirable to adopt concentrated winding methods in which the axial length of the coil ends of the stator coil can be shortened compared to distributed winding methods.